The Most Completely Sampled Rotation Curves for Galaxies

Abstract

We have compiled high-resolution position-velocity diagrams observed along the major axes of nearby spiral galaxies in the CO-line emission, and derived rotation curves for the inner regions of the galaxies. We have combined the inner rotation curves with the outer HI and optical rotation curves to obtain the total rotation curves. The inner rotation curves are characterized by a steep increase within a few hundred pc radius, indicating a compact massive concentration near the nucleus. We fit the obtained rotation curves for individual galaxies by a modified Miyamoto-Nagai's potential by assuming existence of four mass components; a nuclear mass component with a scale radius of 100-150 pc and a mass of $\sim 3-5\times 10^{9}Msun$; a central bulge of 0.5 to 1 kpc radius of a mass $\sim 10^{10}Msun$; a disk with scale radius 5 to 7 kpc and thickness 0.5 kpc of a mass $\sim 1-2 Mgal$; and a massive halo of scale radius 15 to 20 kpc with a mass $\sim 2-3 Mgal$. We discuss the implication of the nuclear compact mass component for the formation mechanism of multiple structures within the galactic bulge during its formation.